The subject matter disclosed herein relates to belts such as those used in elevator systems for suspension and/or driving of the elevator car and/or counterweight.
Conventional elevator systems use rope formed from steel wires as a lifting tension load bearing member. Other systems utilize a belt formed from a number of steel cords, formed from steel wires, retained in a polymer jacket formed from, for example, thermoplastic polyurethane. The cords act as the load supporting tension member, while the jacket holds the cords in a stable position relative to each other, and provides a frictional load path to provide traction for driving the belt.
Elevator belt surfaces need to meet specific performance and life requirements. Two critical requirements are traction within a specified range and wear sufficient to meet life targets, in some instances in the range of 10-20 years. Conventional belts are based on single elastomer jacket materials at the operating traction and non-traction surfaces.
Complex formulations containing elastomers, polymeric additives, waxes, friction modifiers, carbon black and other additives make up the jacket composition. These single formulations are expected to meet all requirements over a range of varying conditions for the life of the belt. However, variations can and do occur owing to changes in surface composition due to temperature, aging and wear. In addition, uneven pressure and slip across a width of the belt can lead to uneven wear. The high wear typically occurs at locations on the belt where the combination of slip and pressure is the highest. The center of the belt is typically subject to high pressure and low slip, the sections of the belt closest to each edge, lower pressure and higher slip.
Complete wearing of a section of the belt down to the inner tension members results in end of life. Strategies have been proposed to develop robust and complex formulations to improve jacket performance. Unfortunately this approach is complex and requires requalification of the jacket material. In addition, the goal of meeting multiple requirements over a product lifetime is difficult.